Synergistic accelerator combinations of phosphorodithioates and thiurams or dithiocarbonates for epdm rubbers



United States Patent US. Cl. 260-79.5 13 Claims ABSTRACT OF THEDISCLOSURE Synergism is shown in the cure-rate factors for EPDM rubberwhen vulcanization accelerator combinations of this invention are used.The combinations consist of a salt of a phosphorodithioic acid combinedwith either a thiuram accelerator or a salt of a dithiocarbamic acidaccelerator.

Background of the invention The invention pertains to the field ofaccelerators for the vulcanization of EPDM rubber. The US. patentclassification is Class 260, Subclass 079.5.

Romieux and Christmann in US. Patent 1,867,631 assigned to the AmericanCyanamid Company (1932) teach the accelerator properties ofdisubstituted phosphorodithioates for the vulcanization of rubber. Thiswork is followed by Andersons in US. Patent 2,879,243 assigned to theUnited States Rubber Company (1959) which reports thiazole acceleratorsactivated by alkali dialkyl phosphorodithioates as acceleratorcombinations for the vulcanization of rubber articles formed from latex.The thiurams are known vulcanization accelerators, for example,tetramethylthiuram disulfide is a commercial accelerator trademarkedThiurad. The salts of dithiocarbamic acids are known accelerators, forexample, zinc dimethyl dithio-' carbamate is a commercial acceleratortrademarked Methazate.

Summary of the invention Synergism is shown in the cure-rate factors forEPDM rubber when vulcanization accelerator combinations of thisinvention are used. The combinations consist of a salt of aphosphorodithioic acid combined with either a thiuram accelerator or asalt of a dithiocarbamic acid accelerator. A fast-curing acceleratorsystem is desirable for EPDM rubber. Shortened times for the cure-ratefactors are shown in EPDM rubber stocks which contain the acceleratorcombinations of this invention in comparison to stocks which contain theaccelerators as single elements. The accelerator combinations of thisinvention provide improved curing systems for EPDM rubber which arefaster curing than the accelerators when used as single elements inEPDM. The salts of phosphorodithioic acids useful in this invention arecompounds of either The R and R in both formulas are straight orbranched alkyl, aryl, alicyclic, alkenyl, aralkyl, or alkaryl radicalsFormula B of less than 19 carbon atoms. R and R can be the same ordifferent radicals. In Formula A, n is 2 when X is zinc, iron, cadmium,tin, or copper. In Formula A, n is 3 when X is iron. In Formula A, n is4 when X is tellurium or tin. In Formula B the amine can be a primary,secondary, or tertiary amine. In Formula B, r is 1 when the amine isdiethylamine, cyclohexylamine, tert-butylamine, monoethanolamine,diethanolamine, triethanolamine, diisopropanolamine,triisopropanolamine, morpholine, piperidine, or3-azobicyclo[3.2.2]nonane. In Formula B, r is 2 when the amine ispiperazine. Some examples of the salts of phosphorodithioic acids usefulin this invention are as follows:

S-zinc 0,0-dibutyl phosphorodithioate S-zinc 0,0-diisopropylphosphorodithioate S-zinc 0,0-dipropyl phosphorodithioate S-Zinc0,0-diethyl phosphorodithioate S-Zinc 0,0-dimethyl phosphorodithioateS-Zinc 0,0-bis(1,3-dimethylbutyl)phosphorodithioate S-zinc 0,0-bisZ-ethylhexyl) phosphorodithioate S-zinc 0,0-bis 4-methylpentyl)phosphorodithioate S-zinc 0,0-ditridecyl phosphorodithioate S-zinc0,0-diamyl phosphorodithioate S-zinc 0,0-diheXyl phosphorodithioateS-zinc 0,0-dilauryl phosphorodithioate S-zinc 0,0-dioctadecylphosphorodithioate S-zinc 0,0-dioctyl phosphorodithioate S-tellurium0,0-di-n-butyl phosphorodithioate S-tellurium 0,0-diisopropylphosphorodithioate S-tellurium 0,0-dipropyl phosphorodithioateS-tellurium 0,0-diethyl phosphorodithioate S-tellurium 0,0-dimethylphosphorodithioate S-tellurium 0,0bis(1,3-dimethylbutyl)phosphorodithioate S-tellurim 0,0-bis Z-ethylhexylphosphorodithioate S-tellurium 0,0-bis(4-methylpentyl)phosphorodithioateS-tellurium 0,0-ditridecyl phosphorodithioate S-tellurium 0,0-diamylphosphorodithioate S-tellurim 0,0-dihexyl phosphorodithioate S-tellurium0,0-dilauryl phosphorodithioate S-tellurium 0,0-dioctadecylphosphorodithioate S-tellurium 0,0-dioctyl phosphorodithioate S-iron0,0-dibutyl phosphorodithioate S-iron O,O-diis0propy1 phosphorodithioateS-iron 0,0-dipropyl phosphorodithioate S-iron 0,0-diethylphosphorodithioate S-iron 0,0-dimethyl phosphorodithioate S-iron0,0-bis( 1,3-dimethylbutyl)phosphorodithioate S-iron 0,0-bis(Z-ethylhexyl)phosphorodithioate Siron 0,0-bis (4-methylpentylphosphorodithioate S-iron 0,0-ditridecyl phosphorodithioate S-iron0,0-diamyl phosphorodithioate S-iron 0,0-dihexyl phosphorodithioateS-iron 0,0-dilauryl phosphorodithioate S-iron 0,0-dioctadecylphosphorodithioate S-iron 0,0-dioctyl phosphorodithioate S-cadmium0,0,-dibutyl phosphorodithioate S-cadmium 0,0-diisopropylphosphorodithioate S-cadmium 0,0-dipropyl phosphorodithioate S-cadmium0,0-diethyl phosphorodithioate S-cadmium 0,0-dimethyl phosphorodithioateS-cadmium 0,0 bis(1,3-dimethylbutyl)phosphorodithioate S-cadmium 0,0-bis2-ethylhexyl phosphoro dithioate S-cadmium 0,0bis 4-methylpentylphosphoro dithioate S-cadmium 0,0,-ditridecyl phosphorodithioateS-cadmium 0,0-diamyl phosphorodithioate S-cadmium 0,0-dihexylphosphorodithioate 0 s-cadmium 0,0-dilauryl phosphorodithioate S-cadmium0,0-dioctadecyl phosphorodithioate S-cadmium 0,0-dioctylphosphorodithioate S-tin 0,0-dibutyl phosphorodithioate S-tin0,0-diisopropyl phosphorodith-ioate S-tin 0,0-dipropylphosphorodithioate S-tin 0,0-diethyl phosphorodithioate S-tin0,0-dimethyl phosphorodithioate S-tin0,0-bis(1,3-dimethylbutyl)phosphorodithioate S-tin0,0-bis(Z-ethylhexyl)phosphorodithioate S-tin0,0-bis(4-methylpentyl)phosphorodithioate S-tin 0,0-ditridecylphosphorodithioate S-tin 0,0-diamyl phosphorodithioate S-tin 0,0-dihexylphosphorodithioate S-tin 0,0-dilauryl phosphorodithioate S-tin0,0-dioctadecyl phosphorodithioate S-tin 0,0-d-ioctyl phosphorodithioateS-copper 0,0-dibutyl phosphorodithioate S-copper 0,0-diisopropylphosphorodithioate S-copper 0,0-dipropyl phosphorodithioate S-copper0,0-diethyl phosphorodithioate S-copper 0,0-dimethy-l phosphorodithioateS-copper 0,0-bis(1,3-dimethylbutyl)phosphorodithioate S-copper0,0-bis(2-ethylhexyl)phosphorodithioate S-copper0,0-bis(4-methylpentyl)phosphoro-dithioate S-copper 0,0-ditridecylphosphorodithioate S-copper 0,0-diamyl phosphorodi-thioate S-copper-O,O-dihexyl phosphorodithioate S-copper 0,0-dilauryl phosphorodithioateS-copper 0,0-dioctadecyl phosphorodithioate S-copper 0,0-dioctylphosphorodithioate Tert butylamine salt of 0,0-di-n*butylphosphorodithioic acid Diethylamine salt of 0,0-di-n-butylphosphorodithioic acid Cyc-lohexylamine salt of 0,0-di-n-butylphosphorodithioic acid Morpholine salt of 0,0-din-butylphosphorodithioic acid Monoethanolamine salt of 0,0-di-n-butylphosphoro-d-ithioic acid Diethanolamine salt of 0,0-di-n-butylphosphorodithioic acid Triethanolamine salt of 0,0-di-n-butylphosphorodithioic acid Diisopropanolamine salt of 0,0-di-n-butylphosphorodithioic acid Triisopropanolamine salt of 0,0-di-n-butylphOsphorodithioic acid Piperazine salt of 0,0-di-n-butylphosphorodithioic acid Piperidine salt of 0,0di-n-butylphosphorodithioic acid 3-azabicyclo-[3.2.2]nonane salt of 0,0-di-n-butylphosphorodithioic acid The thiurarn useful in this invention is acompound of the formula The Rs are alkyl or alicyclic radicalscontaining 1 to 9 carbon atoms. The Rs on the same nitrogen can form aring with the nitrogen atom, and the ring contains from 4 to 9 carbonatoms. In addition, the Rs on the same nitrogen can form a ring with thenitrogen of morpholine or 2,6-dimethyl morpholine. The x can be a numberfrom 1 to 4. Some examples of the thiurams useful in this invention areas follows:

Tetramethylthiurarn monosulfied Tetr-amethylthiuram disulfideTetramethylthiuram trisulfide Tetramethylthiuram tetrasulfideTetraethylthiuram monosulfide Tetraethylthiuram disulfide-Tetraethylthiuram trisulfide Tetraethylthiuram tetrasulfideTetrapropylthiuram monosu-lfide Tetrapropylthiuram disulfideTetrapropylthiuram trisulfide Tetrapropylthiuram tetrasulfideTetraisopropylthiuram monosulfide Tetraisopropylthiuram disulfideTetraisopropylthiuram trisulfide Tetraisopropylthiuram tetrasulfideTetrabutylthiuram monosulfide Tetrabutylthiuram disulfideTetrabutylthiuram trisulfide Tetrabutylthiuram tetrasulfide The salts ofdithiocarbamic acid are a well-known class of accelerators. Someexamples of these compounds useful in this invention are as follows:

Zinc dimethyl dithiocarbamate Zinc diethyl dithiocarbamate Zinc dibutyldithiocarbamate Cadmium diethyl dithiocarbamate Selenium diethyldithiocarbamate Tellurium diethyl dithiocarbamate Piperidiniumpentamethylene dithiocarbamate N,N-di-methylcyclohexylamine salt ofdibutyl dithiocarbamic acid The invention is useful in EPDM rubber. TheAmerican Society for Testing Materials (ASTM) defines EPDM in the 1965Book of ASTM Standards, Part 28, page 695, as follows: EPDM-Terpolymercontaining ethylene and propylene in the backbone and a diene in theside chain. Amberg discusses the dienes which have been used withethylene and propylene in vulcanization of Elastomers 324, 325 (Alligerand Sjothum ed. 1963). Amberg states: Good results have been obtainedwith compounds which have one internal and one terminal double bond.Dicyclopentadiene is one of the preferred dienes. Z-methylene-norborneneand 1l-ethyl-1,1l-tridecadiene are examples of other monomers whichreact satisfactorily. Cyclooctadiene and 1,4-hexadiene are also used asthe diene monomer of EPDM.

Preferred embodiments The curing characteristics in the tables, below,are obtained by testing EPDM with various accelerators and acceleratorcombinations in a Mooney Viscometer and a Monsanto Oscillating DiskRheometer.

The Mooney Viscometer tests are run at C. The Mooney Viscometer is acurerneter with a rotating disk embedded in a rubber sample. The 1 isthe time in minutes required for the Mooney reading to rise 5 pointsabove the minimum viscosity of the rubber sample. The t indicates scorchtime for the EPDM sample. Scorch time is the time required for incipientvulcanization of a rubber sample. The X 4 is a cure-rate factor and isthe time required for an increase of 30 Mooney units above L The MooneyViscometer method of determining curing characteristics has the AmericanSociety for Testing Materials (ASTM) Designation D-1646-63.

The Rheometer is a curemeter with an oscillating disk embedded in arubber sample. The I is the time in minutes for a rise of two rheometerunits above the minimum reading. The 7 indicates scorch time for theEPDM sam ple. The t is the time required to obtain a torque 60% of themaximum. R is the maximum torque and R is the minimum torque. TheMonsanto Oscillating Disk Rheometer is described by Decker, Wise, andGuerry, Rubber World, December 1962, page 68.

The stress-strain data in the tables, showing moduli at 300% elongation,ultimate tensile strength, and elongation are obtained using the methodof the ASTM Designation, D-4l2-64T. The method covers the determinationof the effect of the application of a tension load to a vulcanizedsample of EPDM containing an accelerator at 300% elongation iscalculated as follows:

Modulus at 300% Force at 300% elongation in lbs./in. Originalcrossseetional 6 The compounded EPDM rubber samples of Table 11 containthe following curing systems of accelerators or acceleratorcombinations:

area of the sample 5 Parts by Stock Curing System Weight The data inTable I show curing characteristics dof 1 getrametgyygim-ammonosumge 3EPDv con ainir t ace erat rs tetrameth thiurarn i- 2 etramet yt iurammonosulfi e..- 2.5 t 0 y S-telluriurn0,0-di-n-b11tylphosphorodithioate-0.5 sulfide, zinc dlrnethyi d1th1ocarbamate and S-zmc 0,0-d1- 3Temmethylthiumm monosumde 2 nbutyl phosphorodithioate. The data in TableI illuss-tellm'ium oyQ-di-n-butylph0sph0r0dithi0ate 1 I 4'Ietramethylthmram monosulfirle 1 trate the enhanced effectiveness ofeach accelerator when $.tel1mium oyo di n butylphosphorodithioateu 2combinations of accelerator containing S-zinc 0,0-di-n- 5 s-tellurium Qp sp o u 3 butyl phosphorodithioate are used. The EPDM used in the testsreported in Tables I, II, and III i trademarked TABLE II Ro alene 30l bthe United States Rubber Company.

y y I The EPDM 1s compounded into the followmg master- Minutes Stockbatch. Cure at 160 C. 1 2 3 4 5 Masterbatch ingredients: Parts by weigrM100glecy Scorch at PDM 1 35 L 1 200 t5 30.3 27.3 25.9 22.7 22.8 Carbonb 510k E3345 14.5 10.4 8.5 9.6 18.0

softener Rleometer at160 Zinc Oxide 5 43.8 44.1 42.5 38.0 37.1 3.1 3.23.1 3.1 3.0 Steanc acid 1 10.3 0.2 8.8 7.8 6.7 Sulfur 2 a, 18.5 18.118.7 10.5 24.1 Stress-Strain: The compounded rubber samples of Table Icontaln the Modulus at following curing systems of accelerators oraccelerator 29g? Elonga combinations:

Ultimate Ten- 4 Parts by 30 sile Strength. Stock Curing System Weight;

4 Elongation 1 Tetramethylthluram (l1sulfide 3 2 'Ietramethylthiuramtlisulfida. 2 5 S ZlllG 0,0-di-n-butyl phosph0rod1 102 e 0.5 3Tetramethylthiurarln dlisultlilde-H-i 2 S-zi1e0,0di-n-bnt 0s oro itrioate 1 4 ,,i-,,,, h fi i fifi 1 3 The cure-rate factors (t -t ofstocks 2, 3, and 4 of f tyl p 0 D l 2 Table II illustrate the enhancedeffectiveness of acceler- 5 S-zrnc 0.0d1-n-butylpllosphorodlthwate 3 6Mine PMHPWW} phosphorodithioate 5 ator combmatrons of th1s 1nvent1oncontarnmg S-tellunum i dlmemyl l 0,0-di-n-butyl phosphorodithioate. Eachstock containing 1 Zme dlmethyl dithiocarbarnate 3 an acceleratorcomb1nat1on shows a faster cure-rate fac- TABLE I Minutes Stock Cure atMooney Scorch at Elongation 35 1,150 1,190

60 1,110 Ultimate Tensile Strength 35 1, 290 1,300 1,280 1,180 1,260 401,300 50 1,240 1, 380 1,340 1, 200 1,150 1,200 1,300 60 1,200 Elongation35 250 270 290 330 320 350 210 280 280 300 280 300 280 350 The cure-ratefactors (t -z; of stocks 2, 3, 4, and 6 of Table I illustrate theenhanced effectiveness of the accelerator combinations of thisinvention. Each stock containing an accelerator combination shows afaster cure rate than stocks containing only single elements of thecombinations (stocks 1, 5, and 7). The scorch time (t shown in theMooney data shows a reduction in time for incipient vulcanization forstocks 2, 3, 4, and 6 over the single element curing systems of stocks1, 5, and 7. The time for incipient vulcanization (1 in the rheometerdata is reduced in stocks 2, 3, 4, and 6 over the single element curingsystems.

lowing curing systems of accelerators or accelerator combinations:

Parts by Stock Curing System Weight 1 Tetramethylthiuram monosulfide 3 2Tetramethylthiurarn monosulfide 2 Tertbutylamine salt of 0,0-di-n-butylphos- 1 phorodithioic acid. 3 Tert-butylamine salt of 0,0-di-n-butylphos- 3 phorodithioic acid.

TABLE III Stock 1 2 3 Mooney Scorch at 135 0.:

The Mooney Scorch test was stopped before 3. i335 Mooney unit risebecause the cure was too slow. The cure-rate factor (t -t of stock 2illustrates the enhanced effectiveness of an accelerator combination ofthis invention containing the element the tert-butylamine salt of0,0-di-n-butyl phosphorodithioic acid over stocks 1 and 3. Resultscomparable to those in Table III are obtained with acceleratorcombinations which include the other amine salts of this invention.

Analogous results to those in Tables I, II, and III, supra, are obtainedin EPDM vulcanization when the parts by weight ratio ofphosphorodithioate to 20 parts thiuram or 20 parts salts ofdithiocarbamic acid is varied as much as 0.5 to 60. The preferred rangeis 20 to 40. Optimum properties are achieved with thiuram or salts ofdithiocarbamic acid as the majority proportion. Accelcrating effect isobserved over a wide range of total acceleration, for example, 0.5 toparts per hundred parts of EPDM, but at least 1.0 part per hundred partsof EPDM is preferred. The invention is useful for accelerating non-blackstocks containing clay. The tellurium salts of this invention increasethe EPDM stocks resistance to reversion.

It is intended to cover all changes and modifications of the examples ofthe invention herein chosen for purposes of disclosure which do notconstitute departures from the spirit and scope of the invention.

What is claimed is:

1. A method of vulcanizing sulfur-vulcanizable EPDM rubber whichcomprises:

mixing the EPDM rubber with a sulfur-containing vulcanizing agent and anaccelerating amount of a vulcanization accelerator combinationconsisting of a salt of a phosphorodithioic acid of the formulas R0 1'wherein R and R are alkyl, aryl, alicyclic, aflrenyl, aralkyl, oral-karyl of less than 19 carbon atoms; X is zinc, iron, cadmium, tin, orcopper and n is 2; X is iron and n is 3; or X is tellun'um or tin and nis 4; and A is a primary, secondary, or tertiary amine and r is l or 2;and a thiuram of the formula i i NC-S;-CN

wherein the Rs are alkyl or alicyclic containing 1 to 9 carbon atoms;the Rs on the same nitrogen form a ring with the nitrogen containing 4to 9 carbon atoms; or the Rs on the same nitrogen form a ring with thenitrogen of morpholine or 2,6-dimethylmorpholine; and x is a number from1 to 4; or

a salt of dithiocarbamic acid; and

heating the mixture at a vulcanizing temperature.

2. A vulcanized EPDM rubber product obtained by the method of claim 1.

3. A method of vulcanizing sulfur-vulcanizable EPDM rubber according toclaim 1 wherein the salt of phosphorodithioic acid is of the formulawherein R and R are alkyl, aryl, alicyclic, alkenyl, aralkyl or alkarylof less than 19 carbon atoms; and X is zinc, iron, cadmium, tin, orcopper and n is 2; X is iron and n is 3; or X is tellurium or tin and nis 4.

4. A method of vulcanizing sulfur-vulcanizable EPDM rubber according toclaim 3 wherein the accelerator combination consists of S-zinc0,0-di-n-butyl phosphorodithioate and tetramethylthiuram disulfide.

5. A method of vulcanizing sulfur-vulcanizable EPDM rubber according toclaim 3 wherein the accelerator combination consists of S-zinc0,0-di-n-butyl phosphorodithioate and zinc dimethyl dithiocarbamate.

6. A method of vulcanizing sulfur-vulcanizable EPDM rubber according toclaim 3 wherein the accelerator combination consists of S-tellurium0,0-di-n-butyl phosphorodithioate and tetramethylthiuram monosulfide.

7. A method of vulcanizing sultur-vulcanizable EPDM rubber according toclaim 1 wherein the salt of phosphorodithioic acid is of the formulawherein R and R are alkyl, aryl, alicyclic, alkenyl, aralkyl, or alkarylof less than 19' carbon atoms; and A is diethylamine, cyclohexylarnine,tert-butylamine, monoethanolamine, diethanolamine, triethanolamine,diisopropanolamine, triisopropanolamine, morpholine, piperidine, or3-azabicyclo[3.2.2]nonane, and r is l; or A is piperazinc and r is 2.

8. A method of vulcanizing sulfur-vulcanizablc EPDM rubber according toclaim 7 wherein the accelerator combination consists of thetert-butylamine salt of 0,0-di-nbutyl phosphorodithioic acid andtetramethylthiuram monosulfide.

9. A vulcanization accelerator combination which consists of a salt of aphosphorodithioic acid of the formula P-SH -A wherein R and R are alkyl,aryl, alicyclic, alkenyl, aralkyl, or alkaryl of less than '19 carbonatoms; X is zinc, iron, cadmium, tin, or copper and n is 2; X is ironand n is 3; or X is tellurium or tin and n is 4; and A is diethylamine,cyclohexylamine, tert-butylamine, monoethanolamine, diethanolamine,triethanolamine, diisopropanolamine, triisopropanolamine, morpholine,piperidine, or 3-azabicyclo[3.2.2]- nonane, and r is 1 or A ispiperazine and r is 2; and a thiuram of the formula wherein the Rs arealkyl or alicyclic containing 1 to 9 carbon atoms; the Rs on the samenitrogen form a ring With the nitrogen containing 4 to 9 carbon atoms;or the Rs on the same nitrogen form a ring With the nitrogen ofmorpholine or 2,6-dimethylmorpholine; and x is a number from 1 to 4; or

a salt of a dithiocarbamic acid.

10. A vulcanization accelerator combination according to claim 9consisting of S-zinc 0,0-di-n-butyl phosphorodithioate andtetramethylthiuram disulfide.

11. A vulcanization accelerator combination according to claim 9consisting of S-zinc 0,0-di-n-butyl phosphorodithioate and zinc dimethyldithiocarbamate.

12. A vulcanization accelerator combination according to claim 9consisting of S-tellurium 0,0-di-n-butyl phosphorodithioate andtetramethylthiuram monosulfide.

13. A vulcanization accelerator combination according to claim 9consisting of the tert-butylamine salt of 0,0- di-n-butylphosphorodithioic acid and tetramethylthiuram monosulfide.

10 References Cited UNITED STATES PATENTS OTHER REFERENCES Chem. Abst.,66, 66486 g.

JOSEPH L. SCHOFER, Primary Examiner C. A. HENDERSON, Jr., AssistantExaminer US. Cl. X.R.

